Since graphene was discovered for the first time in 2004, the two-dimensional material has initiated an extensive upsurge of research because of its unique properties. Graphene has excellent mechanical, electrical, optical, thermal performances, etc., and has huge application potentials in many fields, such as transparent conductivity electrodes, supercapacitors, flexible devices, and batteries. However, graphene suffers from no band gap, and therefore cannot be applied to a logic circuit. The two-dimensional materials, such as transition metal chalcogenides (TMDs), MoS2, and WS2, have band gaps in a narrow range of band gap (1.2-1.8 eV), thereby limiting the use thereof in respect of photodetectors. Furthermore, the carrier mobility of TMDs is lower than that of the existing silicon materials and graphene, which also limits its performance in respect of integrated circuits. Thus, developing a novel two-dimensional semiconductor material that not only can make up for the band gap blank between graphene and TMDs, but also has excellent carrier mobility becomes an urgent need.
As a novel two-dimensional atomic crystal material, black phosphorus has an excellent performance, such as a high carrier mobility (−1000 cm2/Vs), a high switching ratio (>105), and a tunable direct band gap (0.3-2 eV), makes up for the performance defects of a zero band gap of graphene, and a very low carrier mobility of transition metal chalcogenides (TMDs), is another two-dimensional material exciting the semiconductor technology and the industrial circle after graphene, has wide application prospects in the fields, such as photoelectric detectors, logic circuits, and batteries, and especially shows great potentials in respect of the development and application of novel photoelectronic devices, such as high-performance optical detectors, optical waveguide, mode-locked laser, modulators, and polarizers.
At present, research and development of the black phosphorus and its preparation technology are mainly focused on intrinsic black phosphorus (e.g., CN104310326A, and CN 105133009A). However, the intrinsic black phosphorus is an asymmetric bipolar p-type semiconductor material, and has both electronic current and hole current, but the carrier concentration and the mobility of electrons are far lower than those of holes, i.e., presented as p-type conductivity, n-type deficiency, and unadjustable carrier concentration, enabling use of the black phosphorus in some fields to be limited. For example, it is not applicable for preparing the complementary metal oxide semiconductor logic circuit (CMOS) and so on. As another example, the intrinsic black phosphorus will, when coming in contact with the metal electrode, have a high schottky barrier, and inhibit the transmission of photogenerated carriers, resulting in a low photoelectric response rate, and failing to contribute to the performance of the photoelectronic device.
How to realize effective control over the p-type and n-type black phosphorus, simply and efficiently build the black phosphorus PN structure having an excellent performance, and then expand use of the black phosphorus in the aspects, such as micro nano-devices, and flexible devices, are the problems expected to be solved for a long time. A lot of researches are made by many researchers in this field. For example, some researchers have prepared a black phosphorus-MoS2 heterojunction. This method needs to strip and transfer MoS2, also needs to use a self-alignment technique, includes a complex process, and results in a low yield. As another example, some researchers have prepared the black phosphorus PN junction using a dual back grating structure, but the method also needs to use the self-alignment technique, and is less efficient.